Rolling process and rolling stand of steel plate

ABSTRACT

A process and a rolling mill for rolling thin plate by means of a tandem rolling mill characterized in that the diameter of either of the upper or the lower working rolls in optional rolling stands situated in the rear step of the tandem rolling mill for thin plate consisting of a plurality of rolling stands is chosen smaller than that of other corresponding working rolls and that the rolling work is carried out by driving only the working rolls with larger diameter.

United States Patent Kamit et al.

[451 Jan. 21, 1975 [54] ROLLING PROCESS AND ROLLING STAND OF STEEL PLATE[75] Inventors: Norimasa Kamit; Ryozi Terakado,

both of Hokkaido, Japan [73] Assignee: Nippon Steel Corporation, Tokyo,

Japan [22] Filed: Nov. 30, 1973 [21] Appl. No.: 420,565

[30] Foreign Application Priority Data Nov. 30, 1972 Japan 47-120057Mar. 28, 1973 Japan 48-35398 [52] U.S. Cl. 72/234 [51] Int. Cl B2lb 1/24[58] Field of Search 72/234, 226, 205, 366, 72/249 [56] References CitedUNITED STATES PATENTS 1,810,167 6/1931 George 72/234 X No.| No.2 No.3

2,139,872 12/1938 Worthington ..72/203 Primary Exam iner- Milton S. MehrAttorney, Agent, or Firm-Torch, McGeady and Stanger [57] ABSTRACT Aprocess and a rolling mill for rolling thin plate by means of a tandemrolling mill characterized in that the diameter of either of the upperor the lower working rolls in optional rolling stands situated in therear step of the tandem rolling mill for thin plate consisting of aplurality of rolling stands is chosen smaller than that of othercorresponding working rolls and that the rolling work is carried out bydriving only the working rolls with larger diameter.

9 Claims, 8 Drawing Figures No.4 No.5 No.6

PATENTED 21 1915 SHEET 1 OF 4 FIG! TI MAX TIMAX Tl MAX No.2 No.3 No.4No.5 No.6 No.7

ROLLING MILL STANDS FIGZ ROLLING MILL STANDS PATENTEU JAN 2 1 I975 SHEET2 [IF 4 FIG.3

FIG.4

PATENTEU 3,861. 188

SHEET 30F 4 ROLLING PROCESS AND ROLLING STAND OF STEEL PLATE SUMMARY orTHE INVENTION The present invention relates to a rolling process toreduce the rolling load and thus enable the rolling of a thinner plateby means of a tandem rolling mill consisting of a plurality of rollingstands, and the rolling stand to carry out the process.

Further the present invention relates to a rolling process to rollcheckered plates such as for flooring which present on the one surfacechecker patterns consisting of discontinuous unevenness or lengthwisecheckered plates which present on the one surface lengthwise checkerpatterns consisting of continuous unevenness.

Until now the tandem rolling mills for thin plates have been developedin such a manner that the production speed has been increasedcontinually. Accordingly the capacity of the motor for driving a rollingmill has increased continually while the diameter of rolling rolls hasalso increased. The above can be said to be reasonable measures in orderto meet the increase of the driving moment, to maintain the strength ofroll necks as well as of components such as spindles, pinion gears anddso on composing the driving system.

However the increase of the diameter of the rolls of a rolling millmeans the decrease of the ratio of the plate thickness to the rolldiameter. In other words, according to the theory of the rollingtechnique the average rolling pressure is greatly influenced by theratio of the plate thickness to the roll diameter so that the averagerolling pressure increases as the ratio decreases. Further the contactlength under the same rolling reduction is proportional to the squareroot of the roll diameter so that the rolling load is all the moreincreased. This will result in the increase of the power to be used forthe same rolling, of the pressure working upon the rolls, of the torqueand so on in such a manner that the smaller the thickness of the platesto be rolled, the more difficult the rolling work becomes. Namelyaccording to the theory of the rolling technique it is desirable toreduce the diameter of the working rolls as much as possible within theallowance of the design. However, the increase of the rolling speed andthe decrease of the roll diameters means the increase of the rotationalspeed of the rolls, which as a result means the significant increase ofrotational speed of the driving system of rolls. This further means theincrease of the rotational speed of motors, which has many problems inthe practical design bringing about an increase of the installationcost. Further in case of a thicker plate, the decrease of the rolldiameter is not as important.

Further, in order to roll the checkered plates, a roll presentinggrooves corresponding to the patterns of the checkered plates as finalproducts has been used as one of the final working rolls of thefinishing rolling mill consisting of a plurality of the rolling standssuch as for example hot strip mills and a flat roll as the other one. Inthe present case the formation of the checker pattern has to be carriedout in only one rolling stand, which means that a comparatively largerolling reduction is necessary to from unevenness with sufficient heighti.e., sufficiently projecting parts. Therefore the grooved roll isexposed to a large rolling load so that the edges of the grooves areoften broken or crushed. In case further steel plates such as those forflooring presenting discontinuous check patterns not parallel to therolling direction are rolled, the rolling work is carried out in adiscontinuous state in such a manner that the roll starts to vibrate,giving off a loud noise. Therefore, the correspondingly large strengthworks between the check patterns to be formed and the grooves of theroll so that check patterns are often inclined along the rollingdirection or often becomes narrow. This causes inferior products.

The purpose of the present invention is to solve the above mentioneddisadvantages of the conventional technics.

BRIEF DESCRIPTION OF THE DRAWING Below the present invention will beexplained in detail according to the attached drawings.

FIG. 1 shows a diagram showing the maximum and the minimum nominaldriving torque of the seven conventional hot strip mill stands (tandemrolling mill for thin plates);

FIG. 2 shows a diagram showing the speed cones of the seven rollingstands;

FIG. 3 shows a diagram showing the actual distances between rolls of thetandem rolling mill consisting of six rolling stands;

FIGS. 4, 5, 6 and 7 show an embodiment of the present invention whereby;

FIG. 4 shows a side view of the whole of the embodiment of a tandemrolling stand;

FIG. 5 shows a front view of the fourth rolling stand of FIG. 4; and

FIG. 6 shows an enlarged side view of the important part.

FIG. 7 shows another embodiment of the present invention, and FIG. 8shows a diagram for the explanation of the effect of the aboveembodiment.

FIG. I shows a diagram showing the maximum and the minimum nominaldriving torques of the finishing rolling stand of the hot strip mill, inthe present example of the tandem rolling mill consisting of sevenrolling stands. The maximum torque naturally takes place in the firstrolling stand and the torque in the third rolling stand is already halfof that of the first rolling stand. Further the torque in the fifthrolling stand is nearly one fifth as low. The same thing can at the sametime be said of the minimum torques of the high rotation speed side ofthe rolling stand.

Namely, T in the drawing shows the driving torques of the rollingstands, whereby T, max. shows the maximum torque of the first rollingstand while T min. shows the minimum torque of the first rolling stand.Along the ordinate of the diagram in FIG. 1 are shown the ratios of. themaximum and the minimum torque of other rolling stands to the maximumtorqueof the first rolling stand, whereby the magnitude is shown in theline a. T max. shows the maximum torque of the second rolling stand,while T min. shows the minimum torque of the second rolling stand. Thetorques of the third to seventh rolling stand are indicated in the sameway.

FIG. 2 shows a diagram showing the speed cones of the seven rollingstands, whereby it is shown that the increase of the speed in therolling stands in the rear step is remarkable. The mark X in the drawingshowsthe maximum rotation speed of the motor, whereby a speed step upmeans is built in the seventh rolling stand to increase the roll speed.The economy of adoption of the high power motor lies in this respect sothat the decrease of the roll diameter presents many disadvantages.

FIG. 3 shows the actual value of the distance t between the upper andthe lower working rolls in case thin plates with 1.2 mm thickness and1.6 mm thickness are rolled in a continuous hot rolling. The presentcase relates to an example of a tandem rolling mill consisting of sixrolling stands. The roll intervals in the diagram shows that the upperand the lower rolls in the third and the following rolling stands arenearly in the contacting states, whereby in the fourth rolling stand theupper and the lower rolls are completely in contact with each other insuch a manner that a remarkable load already exists between the rollsbefore the plate material is put therebetwee. This means that only bymeans of the one working roll the other working roll can be driven inrotation. Namely it is possible to drive reinforcing rolls or otherworking rolls into rotation only by driving one working roll, whereby itis not always necessary to take the roll balance in a case like thepresent.

On the other hand, taking into consideration that the torque in thethird rolling stand of the tandem rolling mill consisting of sevenrolling stands is lower than half of the torque in the first rollingstand, the rolling stand is strong enough even if it is driven by onlyone roll.

The above mentioned fact can commonly be said of the tandem rolling millfor thin plate consisting ofa plurality of rolling stands.

The present invention is based upon the above mentioned consideration,and relates to (1) a process to roll thin plates by means of a tandemrolling stand characterized in that the diameter of either of the upperor the lower working rolls in optional rolling stands situated in therear steps of the tandem rolling mill for thin plates consisting of aplurality of rolling stands is chosen smaller than that of othercorresponding working rolls and that the rolling work is carried out bydriving only the working rolls with larger diameter, (2) a tandemrolling mill for thin plates comprising a plurality of rolling standscharacterized in that the diameter either of the upper or the lowerworking roll at least in one rolling stand situated in the rear step ofthe tandem rolling mill is chosen smaller than that of the othercorresponding working roll and that only the corresponding working rollwith larger diameter is driven, and (3) a method for rolling checkeredplates in which the above roll of smaller diameter is used as a groovedroll.

FIGS. 4 to 7 show an embodiment of the rolling stand according to thepresent invention, in which:

1 shows the upper working roll, 2 the lower working roll, 3 thereinforcing roll, 4 the spindle, 5 the pinion gear, and 6 a drivingmotor. The diameter of the upper working rolls 1' of the fourth and thefifth rolling stand in the six rolling stands shown in FIG. 4 are chosensmaller than that of the other corresponding working rolls, and as isshown in FIG. 5 only the lower working rolls are to be driven. In arolling stand like this, as is shown in FIG. 6 a large rolling reductioncan be obtained by the upper working roll 1' with small diameter.Further, the rolling power hereby is smaller because of the smallerdiameter of the roll. By means of the lower working roll, as large arolling reduction as has been obtained by means of a conventional onecan be obtained, so that as a whole alarge rolling reduction can beobtained. Because in this case a rolling stand in the rear step isconcerned, there should be no problem in the mechanical strength as isshown in FIG. 1, while as large a rolling speed as ever can be obtained.

FIG. 7 shows another embodiment of the present invention and moreprecisely a finishing rolling stand of a hot strip rolling millconsisting of six rolling stands used for rolling a checkered plate.Namely the fourth rolling stand is equipped with a working roll withsmaller diameter than that of the rolls of other rolling stands, wherebyit is characterized that the working roll with smaller diameter isconstructed as a roll with grooves corresponding to the patterns of thecheckered plate. The grooved roll 1" with small diameter is not directlydriven into rotation but by means of the friction with the other flatworking roll set corresponding to the grooved roll 1" with smalldiameter.

In case of the hot strip mill, the checkered plate is, generallyspeaking, in either of the rolling stands in the latter half of thefinishing rolling stands, whereby either the upper or the lower roll isadopted as a grooved roll. In case the rolling stand in question is notthe one in the last step in the finishing rolling stand, the rollinterval of the rolling stands after the one equipped with the groovedroll is chosen so large as to allow the plate to pass through freely,whereby the same thing can be said of the rolling stand according to thepresent invention.

Thus one of the features of the present invention relates to the lastrolling work of the product, and lies in that as a working roll a roll,with grooves corresponding to the pattern of the checkered plates togive the check pattern to the plates is adopted, and the diameter of theworking roll is chosen smaller than that of the other working roll.

According to the present invention a smooth operation can be obtained,by making the roll with small diameter freely rotatable, and not drivendirectly. Nevertheless in case for example the thickness of the platesto be rolled is large, the upper and the lower rolls are brought out ofcontact with each other after the plate has passed through and do notrotate until the next plate reaches, so that there is a danger that someirregularities should take place when the next plate reaches. In such acase, in order to avoid the irregularities the roll balance is cut offimmediately after the plate has passed through and the upper and thelower rolls are allowed to come into contact with each other by means oftheir own weight, to convey the driving power from the working roll, andthe roll balance is inserted immediately before the arrival of thematerial plate in such a manner that the interval between the upper andthe lower rolls is properly adjusted. By operating as mentioned above,the rolling work can be carried out as satisfactorily as in the case theupper and the lower rolls are both driven.

Further the finishing rolling stand of the ordinary hot strip mill iscomposed of quadruple rolls with a back-up roll 3, whereby the presentinvention presents no restriction in the composition of the rolls in therolling stand and further the cutting-off and the insertion of the rollbalance can be carried out so that the present invention can be appliedto any kind of rolling stand without difficulty.

As mentioned above for rolling the ordinary and checkered plates thediameter of one working roll is chosen smaller than that of the otherworking roll so that a large rolling reduction can be obtained at theside of the roll with smaller diameter, thus in case the smallerdiameter roll is a grooved roll, the sufficient height of the unevenpattern namely of the check pattern can be obtained, while in comparisonwith the rolling reduction the rolling load is small so that the powerworking upon the grooves of the roll is reduced, bringing about manyadvantages such as the decrease of the damage of the grooves.

Below the effect of the present invention will be explained according tothe examples.

EXAMPLE 1 The diameter of the upper working roll of the fifth rollingstand in the tandem rolling stand for the 56" inch hot strip millconsisting of six rolling stands is converted into the one with smallerdiameter not to be driven directly. The sizes of the rolls of the thenrolling stand are as follows:

Working roll: 650 mm (1) (standard diameter) Reinforcing roll: 1245 mmHereby the comparison is made between the two cases, i.e., the case Awhen only the diameter of the upper working roll of the fifth rollingstand is chosen as a smaller diameter of 360 mm and the case B when thediameter of both the upper and the lower working rolls is chosen 650 mm.The test piece was a slab (185 mm thick X 930 mm wide, 8.1 ton) of lowcarbon rimmed steel, ordinary very soft steel. The temperature at thetake-in side of the tandem rolling stand was indicated as high as nearly1,100C, the rolling condition of the upper and the lower working rollsof the first to the fourth were rolling stand adjusted same, only theupper working roll of the fifth rolling stand was exchanged for the rollwith the aforementioned diameter, whereby the rolling load of the fifthrolling stand was adjusted by means of the reduction screw in such amanner that the rolling load of the two kinds of rolls indicated by theload cell became the same. The obtained data for rolling is shown inTable 1.

rolling stand of the tandem rolling mill consisting of sevenrolling'stands as shown in FIG. 7. Namely the grooved roll was adoptedas the upper working roll, whose diameter was a standard diameter of 360mm. On the other hand the corresponding lower working roll was a flatroll, whose diameter was 640 mm as usual. The patterns of the groovedroll was checks parallel to the rolling direction, whereby the height(the depth) of the groove was 2.2 mm, the width of the crown 4 mm, thepitch 10 mm and the groove itself was formed trapezoidal. Only the lowerflat roll was driven, whilethe upper grooved roll with small diameterwas left freely rotatable, not to be driven directly. Further the rollintervals of the rolling stands after the fifth one were chosensufficient enough to allow the plate to pass through freely. Thediameters of the working roll were 597 665 mm, while the length of thecylinder was 1422 mm. Further the diameters of the back-up rolls were1150 1245 mm, while the length of the cylinder was 1372 mm.

By such a rolling mill as mentioned above,the test piece of a slab ofvery soft rimmed steel (C: 0.08 percent, Mn: 0.36 percent, 16.5 mm thickx 1260 mm wide) was rolled, whereby the temperature at the taker-in sideof the finishing rolling stand was 11 10C. By properly operating therolling work of the finishing rolling stand several checkered steelplate with thickness (the thickness at deep part) 1.2 4.5 mm wereobtained.

For the purpose of comparison rolling works were also carried out usinga grooved roll with the same diameter as that of the lower flat roll.The result is shown The above mentioned result has proved that byconverting the diameter of the upper working roll of the fifth rollingstand from 650 mm to 360 mmdr and adjusting the rolling load working onthe fifth rolling stand the rolling reduction of 0.62 mm i.e., 1.80 mmdown to 1.18 mm can be obtained according to the present invention whilein the example for comparison the rolling reduction of only 0.40 mmi.e., 1.79 mm down to 1.39 mm can be obtained, whereby a remarkabledifference between both rolling reduction can be observed. As a wholethis means that the finished thickness under the same rolling load isreduced from 1.2 mm down to 1.0 mm, which further means that the verythin plate can be rolled with ease.

EXAMPLE 2 lnthe finishing rolling stand of the 1422 mm hot strip millthe present invention was applied to the fourth Sectional ReductionRatio Section at taker-in side Average section of checkered plateSection at taker-in side Thickness Reduction Ratio Thickness atthickness at deep part taker-in side of checkered plate Thickness attaker-in side ratio while the part B shows that the section is notreduced due to the formation of checks, namely the ratio of the formedchecks, while the same thing can be said of the part A and the part B ofthe curve (II), whereby it is confirmed that the formation of checks isremarkably superior in its ratio in case of the curve (II) relating toan embodiment of the present invention.

What is claimed is:

l. A process for rolling a thin steel plate by means of a tandem rollingmill having a plurality of rolling stands, each stand having an upperworking roll and a lower working roll comprising, reducing the platethrough a plurality of front stands having equaldiameter working rolls,reducing the plate through at least one rear stand having working rollsof different diameters, rotating the working rolls of the first stand ofsaid plurality so as to have the largest torque, and rotating thelargest of said working rolls of said at least one stand following saidfirst stand so that the torque of said at least one stand is less thanhalf of the torque of said first stand.

2. The process according to claim 1, wherein said step of reducing theplate through at least one stand comprises reducing the plate throughtwo stands having an upper working roll of smaller diameter than thelower working roll.

3. The process according to claim 2, wherein said step of reducing theplate through at least onestand comprises forming grooves on one of saidworking rolls of said at least one stand corresponding to a pattern fora checkered plate.

4. A tandem rolling mill for rolling thin steel plates comprising, aplurality of front rolling stands having an upper working roll and alower working roll of equal diameter, at least one rear rolling standhaving an upper working roll and a lower working roll, one of saidworking rolls having a a smaller diameter than the other, means fordriving only the large diameter working roll, the first rolling stand ofsaid plurality having working rolls driven so as to have the largesttorque of all the stands, and said means for driving said largerdiameter working roll driving said roll at less than half the torque ofsaid first rolling stand.

5. The tandem rolling mill according to claim 4, wherein one of saidworking rolls of said at least one rear rolling stand comprises agrooved roll.

6. The tandem rolling mill according to claim 5, wherein said smallerworking roll comprises a grooved roll.

7. The tandem rolling mill according to claim 4, comprising two rearrolling stands.

8. The tandem rolling mill according to claim 7, comprising six rollingstands, said plurality of front rolling stands comprises the first threestands, said two rear rolling stands comprises the fourth and fifthrolling stands, and the sixth rolling stand comprises a rolling standsimilar to that of the first rolling stand.

9. The tandem rolling mill according to claim 4, wherein the torque ofeach stand is progressively lower as the plate travels from the firststand to subsequent stands.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3361188Dated January 21, 1975 Inventor(s) NORIMASA KAMII et a1 It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In the heading of the patent, change:

"[75] Inventors: Norimasa Kamit; Ryozi Terakado,

both of Hokkaido, Japan" "[75] Inventors: Norimasa Kamii; Ryozi Terakadoboth of Hokkaido, Japan" Signed and sealed this 19th day of March 1975.

(SEAL) Atte t:

C. E-LARSHALL DANN RUTH C. E'IASON Commissioner of Patents AttestingOfficer and Trademarks FORM PO-1050 (10-69) USCOMM-DC 60376-P69 1r u.s.sovlnuuiu'r PRINTING omc: nu o-au-Ju.

1. A process for rolling a thin steel plate by means of a tandem rollingmill having a plurality of rolling stands, each stand having an upperworking roll and a lower working roll comprising, reducing the platethrough a plurality of front stands having equal-diameter working rolls,reducing the plate through at least one rear stand having working rollsof different diameters, rotating the working rolls of the first stand ofsaid plurality so as to have the largest torque, and rotating thelargest of said working rolls of said at least one stand following saidfirst stand so that the torque of said at least one stand is less thanhalf of the torque of said first stand.
 2. The process according toclaim 1, wherein said step of reducing the plate through at least onestand comprises reducing the plate through two stands having an upperworking roll of smaller diameter than the lower working roll.
 3. Theprocess according to claim 2, wherein said step of reducing the platethrough at least one stand comprises forming grooves on one of saidworking rolls of said at least one stand corresponding to a pattern fora checkered plate.
 4. A tandem rolling mill for rolling thin steelplates comprising, a plurality of front rolling stands having an upperworking roll and a lower working roll of equal diameter, at least onerear rolling stand having an upper working roll and a lower workingroll, one of said working rolls having a a smaller diameter than theother, means for driving only the large diameter working roll, the firstrolling stand of said plurality having working rolls driven so as tohave the largest torque of all the stands, and said means for drivingsaid larger diameter working roll driving said roll at less than halfthe torque of said first rolling stand.
 5. The tandem rolling millaccording to claim 4, wherein one of said working rolls of said at leastone rear rolling stand comprises a grooved roll.
 6. The tandem rollingmill according to claim 5, wherein said smaller working roll comprises agrooved roll.
 7. The tandem rolling mill according to claim 4,comprising two rear rolling stands.
 8. The tandem rolling mill accordingto claim 7, comprising six rolling stands, said plurality of frontrolling stands comprises the first three stands, said two rear rollingstands comprises the fourth and fifth rolling stands, and the sixthrolling stand comprises a rolling stand similar to that of the firstrolling stand.
 9. The tandem rolling mill according to claim 4, whereinthe torque of each stand is progressively lower as the plate travelsfrom the first stand to subsequent stands.